Likely as another shot at Microsoft, Sony has confirmed that PS Plus will not be required for PlayStation 4 users interested in using the social aspects, entertainment apps, or auto-updates. Xbox 360 users will know that Xbox Live Gold is required for Netflix, Hulu, and social aspects of the console.
It's possible that streaming PlayStation 3 games to the PS4 may require PS Plus, but it seems like that is still up in the air. Unlike the PlayStation 3 which required PS Plus for automatic updates, PlayStation 4 users will find that they get this feature for free.
It seems like some of the PS Plus details for the PlayStation 4 are still under discussion inside the company and are subject to change. This would explain why Sony has detailed the system and PS Plus fully. PS Plus will apply across the PlayStation 3 and 4 for no extra charge.